1. Field of the Invention
The present invention relates to a method for reducing the power consumption of a device including a processor having a multicore configuration and a device for performing the method.
2. Description of Related Art
A conventional general microprocessor incorporates one processor core operating as one component, in which a command issuing section and an operation section are combined in a package. In order to improve performance using such a single processor, a CPU overclock method for increasing clock frequency has been used. However, power consumption increases and heat generation associated with the CPU overclock method becomes a restriction and, therefore, development of another method is needed.
To address the above-described problems, a multiprocessor technique has been developed and widely used such that a plurality of processors are connected so as to operate in parallel with each other and are able to perform an effective process. However, the multiprocessor has the following problem. When a plurality of processors are simply connected together so as to operate in parallel with each other, the multiprocessor becomes large due to the number of processors and, therefore, the utility of the multiprocessor is limited. In an alternative approach, with the recent advance of high-density LSI fabrication techniques, a multicore processor has been developed and widely used in which a plurality of processor cores capable of operating independently from each other are provided on one processor.
In the multicore processor, processor cores can operate independently because of their basically independent configuration. The principle of the multicore processor is almost the same as that of the multiprocessor. A process can be shared among a plurality of processor cores for performance improvement. In other words, an increase in the number of cores provided in the multicore processor leads to higher performance.
For that reason, the number of cores in the muticore processor has eventually increased from a dual-core processor with two cores up to a quad-core processor with four cores. Such a multicore processor is widely known as a user-friendly processor for the following reason. That is, the usability of the multicore processor is little different from that of a multiprocessor configuration, which leads to reliable operation, and it is treated as a plurality of microprocessors by the operating system (OS).
In Japanese Patent Application Publication No. H 11-202988, a technique is disclosed for monitoring the level of use of the respective processors to identify and then stop or suspend a processor which is small in usage, when a multiprocessor system including a plurality of processors does not require a large processing capacity.
In a multicore processor as described above, a plurality of cores are integrated in one processor, and the processor is compact in overall size. Further, the processor is easy to use and has become more inexpensive. High demand for the processor is now expected in small electronic devices. However, when using this high-performance multicore processor, for example, the quad-core processor in which the multicore processor has four cores in one processor, the four cores are not always necessary.
Specifically, for higher performance of a specific electronic device, a high throughput is needed only for a short time in performing a specific function. In the case of mounting a quad-core processor with four cores in a device, when the specific function for performing a large amount of processing is operated, the four cores are in full operation so as to perform the desired function. However, this high-speed process is not required when performing functions other than the specific function.
In the conventional multicore processor, even when the processor has no task to be processed at the moment or does not perform a thread process in one task, the processor always stands ready to perform some processing, which leads to electric power consumption. This useless power consumption is a problem in a general household appliance. Particularly, a large burden exists for a number of devices receiving power from a battery such as a mobile device or lighting devices and on-vehicle devices, and a solution is required. Further, heating increases along with high power consumption, and measures for restricting heat generation and protective measures against generated heat are also required, which increase cost.
In Japanese Patent Application Publication No. H11-202988 cited as related art, the technique merely restricts the operation of a specific processor and does not perform an effective operational control of the entire multiprocessor.